Doping dependence of normal- and superconducting-state transport properties ofNd2−xCex

Abstract

The electric and thermomagnetic transport properties of an underdoped, an optimally doped, and an overdoped c-axis oriented, epitaxial Nd 2Ϫx Ce x CuO 4Ϯy thin film have been investigated in the temperature range from 4.2 K to 300 K and in magnetic fields up to 11 T oriented perpendicular to the CuO 2 planes. In the normal state, the resistivity , Hall coefficient R H , and magnetoresistivity ⌬/(B) can be described quantitatively within a simple two-carrier model if the existence of an electronlike and a holelike band is assumed, where each of the two groups of charge carriers is characterized by a temperature-independent Hall coefficient. A corresponding analysis of the thermoelectric effects appears to be more difficult since they depend on more subtle details of the band structure and the scattering mechanisms. In the superconducting regime, the critical field B *(T) determined from the shift of the resistive transition in an external magnetic field exhibits a positive curvature. In contrast, an analysis of the fluctuation conductivity and the transport entropy of magnetic flux line S consistently gives higher values for the upper critical field B c2 (T). The fluctuation conductivity clearly exhibits two-dimensional scaling behavior, indicating that the quasi-two-dimensional nature of the single-layer compound Nd 2Ϫx Ce x CuO 4Ϯy might be responsible for the difference between B *(T) and B c2 (T). The order of magnitude of S is consistent with the predictions of the Ginzburg-Landau theory. We derived material parameters as B c2 (0), the in-plane coherence length ab (0), the Ginzburg-Landau parameter , and the London penetration depth (0). We also present experimental data on the Hall effect in the mixed state.

Ambipolar Nernst Effect inNbSe2

“…We recall that in electron-doped cuprates, the quasi-particle contribution to the Nernst signal is large and field-linear and can be easily distinguished from the vortex contribution. The large magnitude of the latter (the signal attains a maximum of 0.1-0.2 µV /KT , close to the value found here for NbSe 2 ), has been attributed to the existence of a two-band FS [21,22]. In the hole-doped cuprates, a smaller sublinear Nernst signal is present in temperatures well above T c and can not be distinguished from the vortex signal [1,2,3,4].…”

High-Field Hall Resistivity and Magnetoresistance of Electron-DopedPr2−xCexCuO4−δ

“…Among the distinctive properties, angle resolved photoemission spectroscopy (ARPES) experiments [1, 2, 3] in n-doped cuprates have revealed a small electron-like Fermi surface (FS) pocket at (π, 0) in the underdoped region, and a simultaneous presence of both electron-and hole-like pockets near optimal doping. This clarifies the longstanding puzzle that transport in these materials exhibits unambiguous n-type carrier behavior at low-doping, and two-carrier behavior near optimal doping [4,5,6,7]. Recent low temperature normal state Hall effect measurements [8] on Pr 2−x Ce x CuO 4−δ (PCCO) show a sharp kink of the Hall coefficient at a critical doping x =0.16, which suggests a quantum phase transition (QPT) at this doping.…”

Evidence of ad- tos-Wave Pairing Symmetry Transition in the Electron-Doped Cuprate SuperconductorPr2Biswas1, Fournier2, Qazilbash3 et al. 2002Phys. Rev. Lett.175111210View full textAdd to dashboardCite

“…The value of H c for optimally doped PCCO is about 1000 G at T =1.6 K, taking the coherence length ξ ∼ 60Å [34] and the penetration depth λ about 2500Å [9]. This makes the linear part of the δ − H curve very small and the splitting cannot be resolved at the temperatures of our experiments.…”